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  If your users' e-mail addresses can be computed automatically by simply adding a suffix,
  then specify that suffix. Otherwise leave it empty. Note that users can always override
  the e-mail address selectively. For example, if this field is set to <tt>@acme.org</tt>,
  then user <tt>foo</tt> will by default get the e-mail address <tt>foo@acme.org</tt>
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